A conventional type of drill chuck has a chuck body formed with an axial passage itself having a tapered seat on which three jaws slide. A ring is threaded on the three jaws so that when it is rotated the jaws move axially in the passage to grip the shank of a tool inserted in the passage.
In order to cover the ends of the jaws and to permit hand tightening of the chuck a cover or guide sleeve surrounds the chuck body above the tightening ring and has one end secured to this ring. The ring and sleeve are usually connected together by a simple force fit. In impact-type drills such an arrangement is in sufficiently strong, however, especially in view of the fact that the sleeve in turn is axially coupled to the chuck body. In such devices it is common to form the outer periphery of the tightening ring and the inner wall of the ring with matching grooves in which an eye wire is inserted. This type of connection is not rigid, and is relatively expensive to make.
In my above-cited copending application Ser. No. 377,730 I describe such a chuck wherein the jaws are each formed with two axially elongated teeth having inwardly directed bearing edges which are spaced from each other transversely and are also spaced inwardly of the longitudinal edges of the bearing face of the respective jaw. These teeth are triangular in section and their bearing edges lie on a plane tangent to a cylinder centered on the axis of the tool-receiving hole in the chuck. Between the teeth each jaw is formed with a connecting region which lies wholly radially outside of the respective tangent plane.
With such a structure the facets of a tool of prismatic section are engaged at two angularly spaced locations, greatly stabilizing the tool and preventing twisting thereof relative to the chuck. A tool with a shank of hexagonal section, for example, will have three of its facets each engaged at two separate locations, so that six different regions of line contact with the shank are formed. Similarly a circular-section tool is engaged at three different locations at least, and if the connecting region lies on cylinder centered on the chuck axis and touching each bearing edge, it is engaged at more locations.
In accordance with another feature of my earlier invention, each jaw is formed between its two teeth with a third tooth parallel to these teeth. This third tooth has a bearing edge which lies on a cylinder as described above which is centered on the chuck axis and on which the two outer bearing edges lie. Thus in a three-jaw drill chuck a tool having a circular-section shank can be engaged in nine separate locations. The most secure possible gripping of both prismatic and circular tool shanks therefore is possible.
The drill chuck of my earlier invention generally comprises three jaws angularly equispaced about the axis and having tool-engaging faces which are moved parallel to themselves by a nut rotatably mounted on the body of the chuck which is attached to the shaft of a rotary impact drill by threads formed on outer tapered surfaces of the jaws. The tool-engaging faces each have a pair of main gripping edges or cutting teeth inwardly of the edges of the face and lying on opposite sides of a symmetry plane through the jaw and including the chuck axis. Along this plane is a central edge or cutting tooth which is radially set back from the main gripping edge or cutting tooth so that all three gripping edges or cutting teeth lie along generatrices of a right-circular cylinder centered on the chuck axis. The term, "edge" or "tooth" as used here is intended to describe formations which, at least prior to wear or use of the chuck, have angle profiles, preferably defined by flanks including an angle of at most 90.degree. and, most advantageously, at most 60.degree., the teeth being hardened so as to bite into the tool seized thereby. Each tooth, moreover, is symmetrical about a bisecting plane coinciding (in the case of the central tooth) with the symmetry plane and parallel (in the case of the outer teeth) with the symmetry plane. The grooves between the teeth are likewise of V-section.